BMW’s B38 1.5 litre three-cylinder motor to spearhead new engine family – we test drive it in a 1-Series!

While it may not have always been this way, the three-cylinder engine has pretty much been confined to the K-cars of the Japanese domestic market for a long time.

In Malaysia, you could have a three-cylinder engine, that is if you bought a Perodua with an engine size 1.0 litre and below, but for other manufacturers, they’ve stayed away from three-pot mills so far. For even a 1.1 litre displacement unit, one usually uses a four-cylinder configuration instead. The reason? Noise, vibration and harshness – three-cylinder engines are apparently not very smooth.

But in this age of V8s giving way to six-potters, and six-potters giving way to four-cylinders, everything has changed. The four-cylinder units are being downsized too. All of the sudden, three-cylinders are all the rage again, with Peugeot and Ford recently announcing new three-cylinder families. Fiat even has a two-cylinder engine.

But these are mass market brands. Does a three-cylinder unit belong in a premium brand? Apparently, BMW thinks so, and it also believes it has the necessary engineering prowess to make it work. We were in Munich to learn first hand about its new family of engines, which starts with a small 1.5 litre three-cylinder petrol engine.

The new unit is codenamed B38, and there will also be a diesel counterpart called the B37. From this new three-cylinder engine family will spawn four-cylinder and six-cylinder versions. No mention of an eight-cylinder – this could mean the eight is on the way out or BMW is set to separate the V engine family from the inline engine family.

For this new family, each individual cylinder will have around 500 cc of displacement, as BMW has found that it is a sweet spot between a smaller individual cylinder – which means better acoustics and reduced vibrations – and a larger individual cylinder, which means higher efficiency, reduced friction and less parts. The new cylinders will have a longer stroke and narrower bore compared to current configs, with higher compression ratios.

This means the three-cylinder will be 1.5 litres, the four-cylinder (which will be called the B48/B47) will be 2.0 litres and the six-cylinder (B68/B67) will be a 3.0 litre unit. Simple, right? BMW already has 2.0 litre and 3.0 litre turbocharged engines running on both petrol and diesel fronts, so new versions of those engines will be derived from this new B38/B37 engine family.

The new engine family is designed to be able to be installed in both a longitudinal as well as a transverse position in the engine bay, and they’ll be able to do both front-wheel drive, rear-wheel drive and all-wheel drive. But it’s likely that only the smaller three- and four-cylinder engines will be installed in a front-wheel drive config.

A decade ago, petrol engine turbocharging was a no-no for BMW. Oh, how things have changed. All versions of the engines have TwinPower Turbo technology. What TwinPower Turbo means exactly has been evolving over the years. First, it meant the engine had two turbochargers. Next, BMW extended the use of the term to engines that had a single twin-scroll turbocharger.

Now, the TwinPower Turbo brand name means combining turbocharging with two methods of making an engine both more powerful and more efficient. For petrol engines, the two technologies are Valvetronic as well as High Precision Injection, while for diesel engines you have variable turbocharger geometry as well as a third-generation commonrail technology.

Valvetronic is BMW’s solution for increasing engine breathing efficiency. Though companies like Audi and Honda may disagree, BMW says the solution is a far more effective solution than cylinder deactivation. Munich’s boffins liken it to dimming four lights in a room to achieve the desired lighting instead of switching off two of the four lights.

Valvetronic is claimed to be less complicated and easier to implement on different engine cylinder configurations. A study it did revealed that cylinder deactivation only works 60-70% as often as Valvetronic can.

As for the turbo part of TwinPower Turbo, petrol engines will come with either a single mono-scroll turbo, a single twin-scroll turbo, or twin turbos. The new three-cylinder engine uses the single mono-scroll turbo; BMW says that the torque response of a mono-scroll turbo on the new engine closely matches the response of a four-cylinder twin scroll turbo, in fact bettering it very slightly, as you can see in the graph above.

The diesel engines will have VGT turbos in either a single, twin or triple turbo configuration. We already see this in the current 3.0 litre turbodiesel engine family – when equipped with a single turbo you get a 30d tune, go twin turbo and you get a 40d tune, and finally top it up to the full tri-turbo configuration and you get the 50d engine found in the M550d, X5/X6 M50d and 750d.

BMW’s target output for each 500 cc cylinder is about 40 hp to 67 hp for petrol engines, and for diesel engines it’s 27 hp to 60 hp.

As for torque output, each 500 cc cylinder is expected to produce between 60 Nm to 90 Nm for petrol engines and between 75 Nm to 100 Nm for diesel engines. A range of power and torque output is given, as BMW typically has different tunes for a specific displacement engine, for example the current 2.0 litre four-pot model comes in 20i and 28i tunes.

We’ve calculated the low and high ends of horsepower and torque output for the new family of three, four and six-cylinder engines for easy reference of what the potential can be. Of course, the table above only shows the potential low and high end ranges for output. The various horsepower and torque numbers made available in actual production cars might be anywhere in between the lower and upper end of the numbers shown.

Take a look at the graph below, which shows what BMW thinks is the optimum usage for its new engine family, according to the size of vehicle. From the graph above, it looks like the new 1.5 litre engine is probably set to be used in vehicles that have an upper limit of weight around 1,300 kg and below.

I don’t think it’s an absolute guide though, possibly what would be “right-sized” for the car. There will always be lower-end models with smaller engines and upper-end models with oversized engines for brute power.

For example, given that a 320i currently weighs between 1,475 kg, I suppose this would rule out its usage in such a car, but in reality the power output that the 1.5 litre unit can produce would be more than enough to power the car. In fact, if you look at the current F30 316i, it’s already powered by a 1.6 litre four-pot doing 136 PS. Based on this, I’d say we’ll find the three-cylinder in the 1-Series and 3-Series, in entry-level models.

The new engine family also shares a great deal of parts within the different models – up to 60% between engines that are powered by the same fuel but vary in displacement, and between 30% to 40% between petrol and diesel engines. Even the installation angle and the vehicle interface (connection to the gearbox) is the same.

The company has also built in the possibility for capacity exchange in the production network through interconnected assembly lines, with the four- and three-cylinder petrol and diesel versions having the most flexibility in this regard. This will allow BMW to switch production to different types of engines, enabling swift responses to changing market and customer requirements.

Most importantly from the consumer’s point of view, the point of all of this is reduced fuel consumption. The new engine family is expected to reduce fuel consumption by between 5% to 15%, depending on the configuration of installation.

Anyway, back to the three-cylinder. It enjoys reduced fuel consumption by virtue of its low internal friction, and is nearly 10% lighter and up to 15% more fuel efficient than the current 2.0 litre four-pot. So how does one make a premium three-cylinder engine? There are predominantly two issues to tackle – noise and vibration. According to BMW, the three-cylinder shares a number of common features with the six-cylinder inline engine – neither of them generates free inertial forces, nor free moments of inertia.

The three-cylinder engine is also free of first and second order inertial forces and roll torque, which is very small compared to the six-cylinder engine, is completely eliminated by the use of a single balance shaft. A torsional vibration damper, which works on the principle of a centrifugal pendulum, allows the engine to behave well at low RPMs.

As for sound – that’s where it gets more interesting. We all know the new four-cylinder TwinPower Turbo engines found in the 328i, 520i, 528i etc don’t sound as good as their six- cylinder counterparts. BMW however says the new three-cylinder engine sounds similar to the six instead of the four. At first, I was a little skeptical about this.

The company explains that the frequency of the sound that a three-cylinder engine makes as it revs increases at a rate of about 50% quicker than a four-cylinder unit. To our ears, that’s perceived as being sportier. Basically, an engine produces sounds at various different frequencies. BMW found that the dominant frequency of engine sound of a three- cylinder is close to the range of what a six-cylinder makes, as shown in the graph above.

There are also a lot of secondary frequencies that are produced – the company has used various methods such as exhaust system design to dampen the unwanted frequencies, as well as boost the dominant six-cylinder-like frequency, improving the quality of the sound produced.

Of course, the proof is in the pudding. Graphs and numbers can only say so much. Thankfully, we had the opportunity test drive a car with the three-cylinder engine installed to discover how it actually sounds. The debadged 1-Series you see here runs a prototype version of the B38, mated to an eight-speed Sports Automatic transmission.

Pop the hood and you’ll see the three-cylinder neatly installed as if it were a production car, mounted way back in the engine bay, helping with the weight balance. This same engine bay has to house a big 3.0 litre six-cylinder in the M135i version, so in comparison the 3-cylinder should look tinier than it does here, but the big radiator shroud plastic ahead of the engine masks how much space there is. The B38 engine has a very production-looking plastic engine cover on it, with three “raised stripes” on the right side of the cover where the intake would be, indicating this is a three-cylinder unit.

Our test drive was limited to two laps around BMW’s new 130 hectare BMW Driving Academy in Maisach just outside of Munich, built on what used to be the Furstenfeldbruck airfield. The course was built using cones and consisted of a mix of corners and straights.

The BMW engineers on location revealed that as installed in the 1-Series, the 1.5 litre B38 was doing about 180 PS at 5,000 rpm and 270 Nm of torque from about 1,400 rpm, which is pretty much similiar to the current four-cylinder’s 20i tuning. In Malaysia, we have it installed in the 320i, 520i and X3 xDrive20i. So I suppose if you could give this 1-er a production badge, it would be a 120i.

I haven’t driven a 120i before, so I can’t make comparisons. But I have driven a 520i and an X3 xDrive20i, so I know how the four-cylinder sounds like. And I can tell you that the three-cylinder sounds quite different from the four cylinder. It starts up and settles into a smooth rumble. Start off and you’ll be greeted with a soundtrack that’s growlier and more energetic than the four-cylinder engine – smooth, with no vibrations. You can hear it for yourself in the video embedded here, although I must say that the sound picked up by the camera isn’t really the same as what you hear in real life.

There’s also very little turbo lag, and the power delivery is very linear, which also means the power build up is relatively more progressive compared to the big BAM! from the very beginning that you get with the larger-powered turbo petrol engines like the N54. In this sense, the B38 encourages you to rev the engine as there’s a nice build-up of power to look forward to. The rumble fades into a smoother whine that’s very six-cylinder-like in the second half of the rev range – this is the soundtrack that we all refer to as “sounds like a turbine”.

The car sounds good to the pedestrian as well, and there’s plenty of turbine whine to be heard from the outside, but in the 1-er that I was driving this turbine spool was completely masked out from the interior. I distinctly remember the turbine and recirculating valve being a little more audible in the four-cylinder engine. There’s a really nice exhaust pop during gear changes though, something that BMW gives you when a car is equipped with the Sport AT as opposed to the regular eight-speed AT.

It’s definitely a very interesting engine, and we’re looking forward to the first cars with a production version of the engine to debut. What I couldn’t get to experience during the test drive is how smoothly the engine restarts during auto start/stop operation, as the prototype was not equipped with such a system. Our experience with the four-cylinder engine’s auto restart is not a particularly smooth one compared to the restart of a six-cylinder, so we wonder if the three-cylinder will be jerkier than the four-cylinder.

The introduction of this new engine family should also probably put to rest some rumours that the next generation M3 will be powered by a V6 instead of an inline-6, as we don’t see BMW investing in such a one-off engine to be in sync with efforts to improve production efficiency by commonising parts between these three engine sizes. The next generation M3 might be an M version of the new B68.

With even Audi announcing a 1.5 litre 3-cylinder during the week that I wrote this story, it looks like the three-cylinder is firmly here in the premium segment. I wonder how much smaller things can go.

After dabbling for years in the IT industry, Paul Tan initially began this site as a general blog covering various topics of personal interest. With an increasing number of readers paying rapt attention to the motoring stories, one thing led to another and the rest, as they say, is history. An avid electronic gadget aficionado as well as big-time coffee lover, he's also the executive producer of the Driven motoring TV programme.

personally i dont get all this craze about fuel efficiency. i had the e90 325i and with my heavy footed driving i manage to do 15 mpgs in the city. i sold it for a f30 328i and guess how much mpg i get on average? 18mpg, even though it is advertised to be 35 mpg (again im very heavy footed). so really if you compare the price of the car with the fuel you save (about 50 ringgit a month) id rather if they kept the six cylinders in the 325i and bolt turbos on it, then it will have alot of power and still sound good plus still have reasonable economy. but unfortunately here in malaysia you have to fork out another 200k for six cylinders and turbos (the 335i) even though the price gap is supposed to be only 5k dollars.

Yes, earn more in the sense of currency conversion….try the local tax rates and iva….match that with the cost of living, rental and fuel….a small car with a diesel engine does wonders….btw, diesel at pumps average about RM6.50 at France

Both of your post where u disagree with me, what you are saying to counter my point, is exactly the same shit as i was saying, but worded differently. And this one is especially good, i said tax rate is about the same, and u mentioned about local tax rate.

RM 6.5 in france? This topic has been discussed to bits and yet you are still talking about it. Like i said, you must be thick.

Tell me, if u work and live in france, do you think your employer will pay u in Ringgit?

RM 6.5 is about 1.6 euros. Average income there is 30000-40000 euros per year.
Cars are about 10k euros-20k euros.. Rental is about 200-400 euros per room per month. Decent meals can be had for 5 euros. ( I worked in europe for a few years )

Back to malaysia. Diesel is RM 1.8. Average income is RM30000 or less. Cars how much?
Rental is about RM 500 per room per month. A decent meal costs about RM5-10

And cost of living and buying power? Don’t forget Euro is still a stronger currency compared to Ringgit despite massive problems with their banks.

SO unless you get shafted by your employer earning Ringgit while working and living in France, i suggest you keep such comparisons to yourself, as it simply makes u look like a katak bawah tempurung.

I’m all in for smaller displacement engines in our country. Cheaper road tax and better mileage and I bet there’s enough speed for our roads too. Put this engine into the 3 Series and it could steal sales from the Merc C180.

It’s a pity as BMW Malaysia has no immediate plans to bring in the new 1 Series…perhaps they’re waiting for this engine?

To be honest I can understand why they don’t want to bring this one in. It is UGLY. In a country where beauty is very important that is not a good idea. The only thing that can safe it here is the BMW badge, but will that be enough?

How much smaller can they go? Well, BMW started doing two cylinder engine design studies back in 2008 or 2009, with the aim of developing a unit with a capacity of 500cc per cylinder ( as said in your write up) and an output of 80 or 100 horsepower. The idea at the time was to develop such a two cylinder for future small FWD BM’s. Premium or not, the way things are heading in Europe dictates that manufacturers have to provide vehicles that drink less fuel,meaning smaller engines. Rumours have it that the likes of Mercedes,BM and Audi have 3 cylinder units in development that can squeeze out over 200Hp!

Keep in mind that the Skyactiv engine in the Mazda CX5 is pretty frugal too… according to a German pro VW biased review that I have read it is more frugal than the counterpart from VW, despite the VW having a much smaller engine (1.4 vs 2.2). Large displacement CAN also be fuel efficient, as long as it is a modern engine developed to be so.

I am fine with both methods, though I do admire the tiny high performance engines.

These 3-cylinder engines are developed to meet strict Euro emission standards (all brands have to meet quota within a time frame), it’s got nothing to do with driving pleasure. BMW is simply “conditioning” the media to “accept” this 3-pot engine when it is eventually launched. Years ago, BMW laughed at Mercedes and Audi for making small turbo engines, but how times have changed…anyway, as long as the brand and marketing are strong, you can put a 2-cylinder 660cc engine and BMW would still sell many cars. I mean, does anyone care about the origins of the cowhide used on LV bags?

good write up. these bmw/german engineers is really pushing the envelop of what internal combustion engines can do. can’t wait when they starting to play with electric motors like i3/i8. see how they can push that envelop…

Imagine a bicycle. Diesel engines have longer pedals and because it has longer pedals, the up down motion of your legs are longer as well ( longer stroke, more compression ). And because it has longer pedals, the torque generated when you pedal with the same pedaling force is higher due to simple mechanical advantage.

Diesel engines are torquier simply because diesel has more energy per litre than petrol.

The higher compression ratio is simply due to the fact that diesel combusts at high compression without the need for spark plugs.

Diesel, although has more latent energy, takes a longer time to combust through each stroke, hence they can’t rev very high. To take advantage of that huge but slower explosive torque, engineers design diesel engines with longer strokes to harness that torque and make it more efficient, thus you get the undersquare/long stroke config.

Most petrol cars are done oversquare/short stroke simply because petrol engines (NA) are dogs at low revs. If petrol were more efficient the engineers would’ve used an undersquare config. Larger displacement petrol engines may be designed undersquare, but it all depends on what they’re hauling…

Man. That simply shows one thing. You don’t know much about engineering at all.
The whole engine is built on the principles of thermodynamics. Work cycle, diesel cycle, Otto cycle, atkinson cycle. Work done by expanding gases, torque, moment, gas equations, etc.

Its ok. I won’t debate with you, as debating with you means having to go back to basic form 4 physics, building slowing to advanced thermodynamics and engine building. A knowledge which took me 4 years in Uni to obtain. ALthough i don’t deal with engines in my line of work for 8 years, thermodynamics is an integral part of my work.

No worries. Just believe what you believe. I have no issues with that. I only give explanation, not free education.

To the moron who dead thinks he is right, you don’t hv to click on this and stay ignorant as much as you want.

For the rest of the ppl reading this blog, click on this link, to understand engine operations and why diesels have better torque for the same NA capacity than petrol. ( paragraph 4 )

Since all diesels are turbocharged nowadays, there is another reason why it has more torque is, during the compression cycle, only air is compressed. Hence you can boost the shit out of it preignition doesnt kick in.

3 cylinder engines don sound like that. A power stroke every 240 degrees of crank angle will not get you that sound.

I strongly believe the speakers inside the car is used to generate precise timed sounds to offset the lost harmonics of 3 missing cylinders ( 6 vs 3 ). If noise cancellation headset can work, i don’t think that is beyond the realm of current technology.

This technology is already deployed in the new M5 if im not mistaken.

While i respect the effort taken by BMW/Merc to downsize, but Im concerned that they will take it too far. What’s next? 1 cylinder car?

Just like the HP wars in the early 2000s. Very few ppl would need a car that makes more than 300hp, but BMW/MErc/Audi make them anyway until the point where you get 500-600hp cars that you just cant get enough traction to put those power down.

new era,I wonder hows the performance without those turbos?The Jap got the upper hand on building small cc stock over the Europeans.1.5 3 cylinders turbo that perform better than 1.8 stock but with certain RPM speed of course.

To be honest, I like the 3 cyl engines BMW makes. I mean, it sounds great, no really. It reminds me of the older Austin Mini sound, and I like how old cars (Fiesta, Mini, Escort) sounds like. The 3 cyl BMW make just sounds good. Can’t wait to see it

You can either post as a guest or have an option to register. Among the advantages of registering is once a name has been registered, a guest cannot post using that name. If you have an account, please login before commenting. If you wish to have a profile photo next to your name, register at Gravatar using the same e-mail address you use to comment.